


In Theory

by poselikeateam



Category: Harry Potter - J. K. Rowling
Genre: Alternate Universe - Everyone Lives/Nobody Dies, Alternate Universe - Time Travel, Fix-It, Marauders' Era, Multi, Time Travel
Language: English
Status: In-Progress
Published: 2016-06-26
Updated: 2016-07-23
Packaged: 2018-07-18 07:28:06
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 3,351
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7305211
Author URL: https://archiveofourown.org/users/poselikeateam/pseuds/poselikeateam
Summary: <blockquote class="userstuff">
              <p>Life after the war was rough. Anyone would have expected that. There was a lot for everyone to work through; loss and pain wasn't new to anyone anymore. At this point, more people who'd lived through the war could see Thestral than not. It was... bad. For everyone.</p>
<p>Still, life went on as much as it could. People moved on. They survived. They left the past in the past, as best as they could.</p>
<p>Well, almost everyone.</p>
<p>Apparently the Unspeakables had been working on a project, and of course Hermione had been helping. She was, after all, the brightest witch of her age. It was Hermione who approached Harry and Ron with the idea. It was Hermione who convinced them that they had to take the shot. They had to do it, for everyone, but also for themselves.</p>
<p>The idea was actually pretty simple, in theory. </p>
<p>***</p>
<p>Marauders' Era, time-travel, fix-it AU.  The Golden Trio travel back in time. In theory, the magic should make it seem like they've always been there. Of course, there's always a catch.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> Hey all! I got this idea and figured it wouldn't be too much trouble to run it concurrent with Dark Moons. I've been getting enough good feedback on that one (and thank you so much for it!) that I figured, hey, why not? Sure, this is a real tired-out cliche, but let's see if I can't do something new with it, yeah? Ratings/pairings/warnings might change, but I don't really know yet. I hope you enjoy it!

Well. This was... something. 

Harry James Potter, saviour of the Wizarding World, Boy Who Lived Twice, Auror, Youngest Seeker in a Century, Man With Too Many Fucking Nicknames, thought that once the war ended, these Situations would stop. He was sick of getting stuck in weird situations that would never, in a million years, happen to anyone else; the misadventures and self-sacrifice and just plain weird, impossible shit he dealt with since the day he deflected the Killing Curse on Halloween, 1981. 

He'd faced a Mountain Troll, a Cerberus, a killer chess set, and a teacher with Voldemort grafted onto the back of his skull at age 11. He'd faced Acromantulas, a Basilisk, and an eternally-young piece of the Dark Lord (which was trapped in a diary and feeding on an 11 year old girl) at age 12. At 13 he cast his first Patronus. He'd survived all three Unforgivables, destroyed more Horcruxes than anyone had ever seen, ridden Thestrals, won the Triwizard Tournament, explored the Department of Mysteries, escaped Fiendfyre, and watched almost everyone he loved die. 

That last part was what brought him here. Or rather, now. It was all actually very complicated. 

Harry Potter. That name meant nothing here and now, and he was honestly more weirded out by that than he thought he would be. Well... less weirded out by that, and more the fact that he was currently at Hogwarts in 1978. 

It shouldn't be that strange. After all, it wasn't as if he hadn't known this was going to happen. He'd signed up for it. Well, he'd actually _been_ signed up for it, but he'd agreed to it, and that was the important part. The point was, he knew it would happen. Still, it was different, knowing it in theory and actually experiencing it. 

When he woke up, he was in the Gryffindor dorms again. Merlin, he hadn't been there for years. Not since... Well. He wasn't going to think about it, because it didn't matter. Apparently to everyone else, he'd been there for the past six years, and was just starting his seventh, which meant that he was 17, so thank Hecate for small miracles. If he had to be any younger, he wouldn't be able to handle it. A decade was enough, thank you very much.

He also expected-but-did-not-expect everyone acting like it was totally normal for him to be there, like he belonged there, like he'd really been there the whole time. Still, it was a bit of a shock to see all the Marauders there, alive and younger than him. Er. His age. 

This was going to be strange.

***

So it went like this. 

Harry Potter, Ron Weasley, and Hermione Granger worked in the Department of Magical Law Enforcement. Harry and Ron were Aurors. Hermione... well, no one was quite sure what she did; probably a bit of everything. She gave a different answer any time someone asked. The only answer she gave twice was "classified". 

Life after the war was rough. Anyone would have expected that. There was a lot for everyone to work through; loss and pain wasn't new to anyone anymore. At this point, more people who'd lived through the war could see Thestral than not. It was... bad. For everyone.

Still, life went on as much as it could. People moved on. They survived. They left the past in the past, as best as they could.

Well, almost everyone.

Apparently the Unspeakables had been working on a project, and of course Hermione had been helping. She was, after all, the brightest witch of her age. It was Hermione who approached Harry and Ron with the idea. It was Hermione who convinced them that they had to take the shot. They had to do it, for everyone, but also for themselves.

The idea was actually pretty simple, in theory. Hermione had used a Time Turner, and understood it well enough that she had figured out how to recreate one. The difference, however, was that instead of each turn taking the user back one hour, it took them back one year. If they went back far enough, they could stop Voldemort before he got too powerful and make sure that things didn't change too much besides that. 

They finally decided that they should go back to 1978. They knew what Horcruxes Voldemort had and hadn't made by then, and where he'd hidden them. Enough scrying had been done by the Unspeakables in the Hall of Prophecy to help them with that. That was also when Voldemort had began gathering the most followers, but hadn't begun to act yet. In theory, the Time Turner's enchantments should have made it seem as though they belonged there, had always been there. And for the most part, that was true.

However, Harry ran into problems the first morning.


	2. Chapter 2

**Notes for the Chapter:**

> Now that I've figured out a it where I want to go with this, I figured I'd try to update it. I've got a busy work schedule coming up, so I may not be able to work on either this or Dark Moons for a few weeks.

Harry tried to pretend that everything was normal when he found himself shoved into a room with his father, his godfather, and their two best friends, even though seeing Peter again after all these years filled him with rage and seeing the other three filled him with tears. 

"You alright, mate?" Sirius - seventeen year old Sirius - asked, clapping him on the shoulder. 

"Er, yeah," Harry said, coughing a bit, trying to hold back all the feelings slamming into him like the Whomping Willow. "Just... weird dreams."

Remus gave him a sympathetic look (he missed those, missed Remus). "I know how that goes. Need anything?"

Harry shook his head. "Just breakfast," he said, forcing a grin. "I've forgotten most of it already, anyway." 

Sirius barked a laugh. "Good show, Potter!"

James' head snapped up. "What?" he asked.

"Not you, Prongs dear," Sirius said, rolling his eyes. "Your brother."

"My _what_?" James snapped, gaping. 

"Your brother," Sirius answered slowly. "You hit your head last night?" 

James looked at Sirius a bit longer, then glanced at Harry, then stared. "Oh," he said. "Yeah. Don't know how I'd forgotten."

Sirius snorted. "You've lived with the bloke for 17 years now; you'd think you'd remember your own twin brother."

"Had a rough night," James muttered, still staring at Harry. "Weird dreams."

"Ooh," Peter teased, making both James' and Harry's heads snap up towards him. "It's like you have that twin telekinesis!"

"I'm pretty sure you mean telepathy, Pete," Remus said, frowning at the strange exchange between his friends. 

Peter waved his hand. "Right, right. That. Whatever - I'm starved." He picked up his bag and headed towards the door. "C'mon, before Longbottom eats all the bacon."

"Pretty sure Frank couldn't eat a hundred pounds of bacon," Remus said, though he made to follow.

"Not for want of trying!" Sirius laughed. He looked to the Potters. "You blokes coming, or what?"

Harry ran a hand through his messy hair. "Give me a bit to put my robes on, you nutter," he answered, surprised at how easily the words came. The spell probably affected him as well as everyone from the past, adding familiarity so he wouldn't stick out. It seemed like the sort of detail Hermione would add to something.

James glanced at him, then at his friends. "I'm gonna wait for my idiot brother," he said, seeming surprised at his own words as well. That... was not a good sign, Harry decided. Why didn't James seem to recognise his "brother" Harry? "You go on ahead."

The other Marauders looked at them, shrugged, and left, shouting back their goodbyes and no promises to save them any bacon. 

The door was barely shut a moment before Harry felt himself pulled up by the front of his nightshirt and pushed against the wall, wand at his throat. Green eyes met hazel, as two otherwise nearly identical faces stared at each other, taking everything in. "Alright, 'brother' mine," James all but snarled. "I don't know who the fuck you are or how you've tricked everyone else, but I suggest you start talking. Fast."

Harry's heart and mind were racing. "Shit," was all he said. "Da-- James, mate, put me down."

James' eyes narrowed. "What was that you were about to call me?" he asked.

"N-nothing. You're acting crazy. How can you not remember your own brother--?"

"Because I'm an only child, you tosser!" James snapped. "Always have been. No only child wakes up and suddenly has a twin everyone but him can bloody remember!"

Harry sighed. “At least put me down. Keep your wand on me if you like - Merlin knows I would - but maybe if you weren’t half-choking me I’d feel a bit more inclined to talk.”

James glared for a few seconds, then let go, wand still pointed at Harry’s throat. “One wrong move,” he said, “and I’ll curse your pants off.”

“Your call,” Harry said. “Can I at least sit down?” When James nodded, Harry sat on his bed. “I don’t even know where to begin, you know. It might be smoother if you just asked your questions first.”

“Who are you, really?”  
Harry made a face between grimace and grin. “Go for the hardest question first? Practise hard, game easy, eh?” 

“Our Quidditch captain says that,” James said.

“I know,” Harry answered. “Somehow. I… think I’m Gryffindor Seeker.”

“You don’t remember any of this either?” James’ wand lowered a fraction of a centimetre.

“Not really. Vaguely. In pieces, if I try. It’s all very strange, but it always is with Unspeakables.”

“Unspeakables?” James repeated. “So you’re from the Ministry?”

“In a sense. I’m… er, I was an Auror. Or I will be.”

“What in Merlin’s name is that supposed to mean?”

Harry shrugged. “It’s not making much sense to me either, but if I explain, you won’t believe me. I’ll bet you 20 Galleons.”

“You’re on,” James said. “Try me.”

Taking a deep breath, Harry said, “Alright. My name is Harry James Potter. I’m your son, from the future. I was sent back in time to stop Voldemort before he got too powerful but late enough that the Wizarding World would learn its lesson and no one would repeat his extremism for a while. A lot of people died in the Second Wizarding War, as it’s come to be called, as well as the first. I, er, sort of won the second, in a way, by killing him, but it was really everyone at the Battle of Hogwarts more than it was me. You and Mum died when I was a baby, when he killed you and I survived the Killing Curse, marking me as the Chosen One who was supposed to stop him. There was a prophecy. It hasn’t been issued yet. Sirius was wrongly accused of selling you to Voldemort and spent twelve years in Azkaban, even though it was Pettigrew,” Harry spat his name, “who did it. Remus died at the Battle of Hogwarts. I’m an Auror, as well as my two best friends, Ron Weasley and Hermione Granger. Hermione was working with the Unspeakables, which is how the three of us were sent back, with a prototype Time Turner, since almost all of them had been destroyed in 1995. Their magic was supposed to actually alter time, so it seemed like we belonged here; but somehow, it didn’t work on you. I… I’m probably missing a lot, but that’s it. The truth.”

There was a long pause. “You know,” James finally said, “I almost want to say I believe you, if only so I can win the bet.”

Harry snorted. “I told you. I wish there were some way I could prove it, but I don’t know how.”

James lowered his wand. “I think I know a way. Give me two days. If you cause any trouble, I will absolutely hex your pants off.”

Harry snorted again. “The great James Potter, Marauder, tells me not to cause trouble?”

“You know what I mean,” James snapped, though a smirk was threatening to pull at his lips.

“Alright,” Harry said. “I don’t mean any trouble, anyway. Two days. What… what day is it?”

“Thursday,” answered James. “Be ready on Saturday, alright, ‘brother’?” 

Harry nodded. Whatever James had planned, he was ready to play the waiting game.


	3. Chapter 3

**Notes for the Chapter:**

> I don't know how clear this was, but the chapter starts at the end and then ends where I started? Like, it comes full circle. I don't know. I've been working a lot lately. I hope you enjoy this - it's wonderfully weird to write.

"Merlin's hairy left nipple," breathed James.

The last few days had been... well, he could say normal, but they weren't. At all. First, he woke up to see someone who everyone but him remembered as his twin (though he insisted to himself that he was an only child) and looked almost exactly like him, but for the eyes. They were the same shocking green that Lily Evans had. Ah, Evans. So beautiful, as fiery as her hair and untameable as his hair without his father's patented Sleekeazy's Hair Potion. 

He shook himself. Now was not the time to think about the Gryffindor Head Girl (well, every time was the time to think about Evans, but that was a different point altogether). At the very least, not in that way. What was important was that she, too, didn't remember this supposed twin of his. 

"Potter," she said in that curt way of hers that told him that he was about to be in trouble with her again. She grabbed the sleeve of his robes and pulled him aside before he could say anything. He had been on his way back from the Great Hall, but no one paid either of them any mind; they were as used to this as he was.

"Evans," he said flirtatiously (ignoring the nagging voice in his head that said this definitely wasn't the time). "Before you start, I'd like to postulate that it's too early for me to have done whatever it is that's bothered you this time."

She scowled at him. "There are two of you, Potter. Explain." She must have noticed the shocked look on his face, because she continued, "I don't know how you got everyone to act like he's been here all along, but I'm not buying it. This gaslighting shite isn't funny, and I--"

"Whoa, whoa, Evans," he said, holding his hands up defensively. "I swear on my life, I had nothing to do with this. I'm still trying to figure it out, as well." He paused. "It's... odd. I thought I was the only one who knew something was wrong."

"You expect me to believe you had nothing to do with this?" she snapped.

"Yes, I do, because I own up to my pranks. You know that."

She faltered. "That... that you do. You always have. What do you think it is, then?"

James shrugged. "I'unno. He said he was from the future, if you can believe it - I can't. I don't trust him, but I have a plan."

Lily groaned. "No. Whatever it is, you can't."

"Evans," he snapped, "you don't understand. Whatever he's done, wherever he's from, whoever he is, he's convinced all of Hogwarts that he's been here for seven bloody years. Everyone. He's convinced my three best mates that he's my twin brother, for Merlin's sake! Even Dumbledore didn't bother to so much as glance at him. That's some pretty powerful magic."

There was a long pause, before Lily sighed. "You're right. But why isn't it affecting us?"

"I would love to know, believe me," said James, frowning. "If you're willing to find out, let me know, and I'll tell you my plan. If not, I won't risk you mucking it up by going to McGonagall. He could be dangerous. I'm not risking it."

"When did you get responsible?" she snorted. 

"I am capable of seriousness, when the situation demands it," he said with a wink. "Now, are you in or out?"

There was another long pause, in which Lily crossed her arms and tapped her foot, thinking. "Fine," she finally said. 

So he told her of his plan to steal a vial of Veritaserum from Slughorn's office, which she immediately decided was "absurd". He would notice a Ministry-controlled substance disappearing, and anyway, they wouldn't need an entire vial. He argued that there would be no way to filch exactly three drops, and Lily just flipped her hair over her shoulder and told him that there was always a way.

The next day they met up and Lily transfigured an old quill into an eye dropper - she was really an amazing witch, he thought, only swooning a little - and told him to use that while she distracted Slughorn. 

So, James slipped into his Invisibility Cloak and went to the potions cabinet, whispering a quick _Alohomora_ when Lily gave the signal (which was tapping her book on her thigh). Since Lily was a star student and they weren't really what one might call 'friends', Slughorn wouldn't be on the lookout as he would if one of the Marauders were talking to him about extra credit. As Slughorn assured her that she didn't need it, and she insisted that she wanted more practise with more difficult potions, James slipped a small amount of Veritaserum into the eye dropper and swiftly yet quietly shut the door. He then sneaked over to the door, pulled off his cloak, stuffed it into his bag, and knocked on the door. 

Slughorn opened it, seeming surprised that James was at his door. "Is Evans here?" he asked. "Marlene said she would be, and I need to talk to her, Head Boy to Head Girl." 

"Well," he said, "yes, but..." he turned to Lily. "Could we continue this later then, my dear?"

"Of course, Professor," she said with an all-too-charming-and-demure smile. "Perhaps after the next Potions class, if you have a free period?"

"That I do," he said. James rolled his eyes, which Slughorn apparently missed, but Lily did not. 

And that was how the Gryffindor Head Boy and Girl stole a Ministry-controlled substance from a Hogwarts professor. They agreed to meet up the next day with this Harry fellow, who'd been acting so much like a normal student that they were only more suspicious. Both watched him like a hawk until then, each finding different excuses, until that moment arrived. James brought the other two to the Room of Requirement, and it became an interrogation room (much to his chagrin and Harry's amusement). They administered the potion and waited.

Once it had taken hold, they asked their questions. 

"Who are you?" asked James.

"Harry James Potter," said the other, dreamily. "Your son."

"Whose son?" asked Lily incredulously.

"Yours. And his. Both of yours."

"That's impossible," James said.

"Yes, but he can't lie," Lily snapped.

"It must be tainted!" James snapped back.

"What year were you born?" Lily asked, eyes narrowed.

"1980," answered Harry.

"That- that's two years from now," Lily said, looking from Harry to James.

"Why does everyone recognise you but us?" James pressed on.

"I don't know. You should have, too."

"No," Lily said. "Why does everyone else recognise you?"

"The Unspeakables sent us back, after the War. Wanted us to fix everything. The enchantment was supposed to make it seem like we belonged, so we could stop Voldemort without trouble."

"We?" asked James. "There are more of you?"

"Ron Weasley and Hermione Granger," answered Harry. "My two best friends."

"Ron and Hermione? But that doesn't make sense... I know them. Or, I thought I knew them," whispered Lily.

"Me too, but let's focus on him and figure it out later. He mentioned a war."

"What war?" Lily asked.

"The Second Wizarding War," said Harry.

"And now? This is the beginning of the first, I assume?"

"Yes."

"What ended the first?"

"You died. He couldn't kill me." Harry looked at Lily. "Your love saved me from the Killing Curse. Nothing saved you."

Lily covered her mouth with one hand. "How old were you?"

"One."

Things went on like that, and James and Lily learned everything they could about the future they apparently didn't have. They learned how Petunia and her future husband and son abused their future son when they were gone. They learned about their friends' deaths. They learned about everything Harry had gone through, everything the world had gone through. By the end, Lily was crying (and apparently didn't realise it) and James was... numb. 

"Merlin's hairy left nipple," breathed James.


End file.
